Tuning depends on the sound source. If you are using a sound card/synth that can be tuned (Roland VSC, Creative SoundBlaster, and others), you may be able to tune it using the Master Tuning feature in Band-in-a-Box®, under the GM menu. If this does not work, see your sound card/synth manufacturer for support. If you are using a synth module or keyboard, see the manual for tuning info.
If Band-in-a-Box® is playing out of tune, and you are using a software synthesizer (rather than a hardware synth/module), your sound card itself could be out of tune. Test this by playing MIDI and wave files with Windows Media Player, outside of Band-in-a-Box®. You will need to contact the computer or sound card manufacturer to resolve this problem.
Another possibility is that your sound card is locked at a different sample rate than Band-in-a-Box® supports. Band-in-a-Box® plays audio using 44.1 KHz sample rate. If you sound card is locked at 48 KHz (for some reason), then the audio will be playing at the wrong pitch.